Such a device is utilized, for example, in a single-sheet printer in order to convey single sheets of paper from one processing station to a next processing station. More recent printers require a plurality of such conveyor devices, so that the demand for high operating dependability is made of these. It can occur in traditional conveyor devices that, given imprecise guidance of the leading edges, of the trailing edges and of the side edges of a single sheet, a corner of the single sheet can be bent over and the corner that has been bent over, what is referred to as a "dog ear", is fixed in the fashion of an ironing procedure due to the transport of the roller and counter-pressure roller lying opposite one another. Such a bent-over corner leads to a reject or can lead to a paper jam in the printer over the course of the further conveying path. It is therefore desirable to increase the operating dependability of such a conveyor device.
U.S. Pat. No. 5,040,781 discloses a device for conveying sheet material that is not flat, for example envelopes. The counter-pressure roller of this device has channel-shaped recessed in which the longitudinal edges of the envelope proceed. An obliquely guided envelope thus does not cause a conveying jam.
German AS 22 55 920 discloses a device for conveying card-shaped data carriers. The device has a driven roller that has a free-running counter-pressure roller residing opposite it. The data carriers are conveyed in the conveying nip between the two rollers.
DE-A 39 30 737 discloses a paper conveying means for printer devices, whereby paper is conveyed in the conveying nip between a driven roller and a counter-pressure roller that is likewise driven. The roller and the counter-pressure roller have recesses into which guide plates that supply the sheet-shaped material to the generated surfaces of the roller and the counter-pressure roller project.
Patent Abstracts of Japan, vol. 016, No. 195 (M-1246), May 12, 1992 and JP-A-04 028640 (Canon, Inc.), Jan. 31, 1992, disclose a paper guide unit wherein a counter-pressure roller has channel-shaped recesses into which tongues of a pressure plate engage. During operation, a single sheet is conveyed along the circumference of a conveyor roller in the conveying nip between conveyor roller and the pressure plate. The tongues engaging into the channel-shaped recesses of the counter-pressure roller guide the single sheet to the circumferential surface of the counter-pressure roller.
U.S. Pat. No. 3,957,366 discloses a paper delivery means wherein conveyor rollers residing opposite one another contain channel-shaped recesses.
Nose-shaped sections that are bent off at their ends and that have two operating positions project into these recesses. In the one operating position, the bent-off ends serve as detents that hold the single sheet at the front end edge, so that it arcs up given continued conveying. In the other operating position, the sections are lifted so that they release the single sheet and it is further-conveyed by the conveying nip formed by the rollers. The nose-shaped sections serve for aligning the single sheet, so that, after being supplied slanting, it can be further-conveyed with correctly aligned end edge.
U.S. Pat. No. 5,147,274 discloses an alignment means for sheet material. The sheet material is conveyed between rollers residing opposite one another. The longitudinal edges of the sheet material run freely between roller elements.
Therefore, there is a need for a device for conveying sheet-shaped material that works disturbance-free with high dependability.